Spray guns are widely used in vehicle body repair shops when re-spraying a vehicle that has been repaired following an accident. In the known spray guns, the liquid is contained in a reservoir attached to the gun from where it is fed to a spray nozzle. On emerging from the spray nozzle, the liquid is atomized and forms a spray with compressed air supplied to the nozzle. The liquid may be gravity fed or suction fed or, more recently, pressure fed by an air bleed line to the reservoir from the compressed air line to the spray gun.
Traditionally, the liquid is contained in a rigid pot mounted on the spray gun by engagement of complementary screw threads on the pot and gun. In this way, the pot can be removed for cleaning or replacement. Typically, the pot is secured to the gun empty and has a removable lid by means of which the liquid can be added to the pot while attached to the gun. On completion of spraying, the pot can be removed and the gun and pot cleaned for re-use.
Such screw threaded connection requires the reservoir to be rotated several times, typically at least four or five turns, to engage fully the threads and secure the reservoir in a fluid tight manner. This is time consuming and requires considerable care and dexterity on the part of the user to prevent spillage when the reservoir is full of liquid.
Furthermore, the threads on the gun and pot may be damaged by miss-use, for example if an attempt is made to secure a pot having a non-matching thread. Also, on completion of spraying, careful cleaning is required to remove all traces of liquid from the threads to prevent the threads becoming blocked, for example with dried paint, and to prevent cross-contamination with the liquid next sprayed.
Damaged or blocked threads may render the gun unusable requiring the purchase of a new gun. This adds to costs and is inconvenient if time is lost because a spare gun is not to hand to continue spraying. Moreover, cleaning of the threads usually requires solvents that are also used to clean the gun and pot. The use of solvents is undesirable from health and safety considerations and causes problems for disposal of the solvent after use.
In order to reduce these problems we have developed a system for connecting the reservoir to the gun via a releasable quick-fit connection employing bayonet type formations that are engageable with a push-twist action requiring less than one complete turn of the reservoir to connect/disconnect the reservoir.
This arrangement enables the reservoir to be attached to and detached from the gun in a simple, efficient manner that requires less dexterity on the part of the user. Accidental release of the reservoir may occur however if the integrity of the connection is compromised.
For example, in a suction feed spray gun, the reservoir hangs vertically down under the gun and unintentional separation of the reservoir from the gun may occur if the reservoir is inadvertently rotated to a position in which the reservoir can fall under gravity.
In a gravity feed spray gun, the reservoir is located on top of the gun and accidental separation of the reservoir from the gun may also occur if the reservoir is inadvertently rotated to a position in which the reservoir can fall under gravity if the gun is tilted or inverted.
Accidental release of the reservoir leading to separation of the reservoir from the spray gun may result in paint spillage requiring cleaning and possible re-working of the surface being sprayed. This adds to costs both in terms of the materials used and the time taken to spray the surface to achieve an acceptable finish.
Even if the reservoir does not physically separate from the spray gun, the efficiency of the fluid-tight seal between the reservoir and gun may be reduced resulting in leakage of paint requiring cleaning of the gun and/or reservoir and possible re-working of the surface being sprayed.